Staff Perspectives on Implementation of Long-Acting Injectable Preexposure Prophylaxis at a Low-Barrier Syringe Services Program in Philadelphia, PA

Abstract

Introduction

Long-acting injectable cabotegravir (CAB-LA) for preexposure prophylaxis (PrEP) is a promising HIV prevention tool for people who inject drugs (PWID), who face elevated HIV risk and barriers to care. While acceptable to PWID, CAB-LA implementation in low-barrier syringe services programs (SSPs) has not been examined.

Methods

From August 2023 to July 2025, we conducted semistructured interviews with 12 SSP staff involved in CAB-LA delivery. Interviews were transcribed and analyzed using thematic analysis guided by the Consolidated Framework for Implementation Research.

Results

Facilitators included CAB-LA's relative advantage over oral PrEP, external technical support, 340B pharmacy revenue, alignment with SSP mission and workflows, motivated staff, and financial incentives. Barriers included lack of FDA approval for PWID, complex logistics, performance pressures, infrastructure constraints, competing priorities, staff workload, and client outreach and engagement.

Conclusion

Integrating CAB-LA into SSPs is promising, but successful implementation requires targeted strategies, including additional resources, workflow adaptations, and enhanced outreach.

Plain Language Summary

Staff perspectives on implementation of long-acting injectable pre-exposure prophylaxis at a low-barrier syringe services program in Philadelphia, PA

People who inject drugs (PWID) are at high risk for HIV but often face major barriers to prevention and care, such as stigma, unstable housing, and limited access to health services. Syringe services programs (SSPs) are trusted, low-barrier settings where PWID can receive health care. A new HIV prevention tool—long-acting injectable cabotegravir (CAB-LA)—is highly effective and may be easier for some people to use than daily oral preexposure prophylaxis (PrEP) pills. However, little is known about what helps or hinders the delivery of CAB-LA at SSPs.

To explore this, we interviewed 12 staff members (both clinical and non-clinical) at a Philadelphia SSP who were directly involved in CAB-LA implementation. Staff described benefits, including that CAB-LA meets PWID needs better than oral PrEP, aligns with the SSP's mission, brings revenue through a pharmacy partnership, and is supported by motivated staff. They also described challenges, such as the lack of FDA approval for use with PWID, complicated logistics, limited space and staffing, competing program demands, and difficulties maintaining client engagement.

Overall, staff saw CAB-LA as acceptable and valuable for PWID, but overlapping challenges made implementation difficult. Addressing these barriers through additional staff and financial resources, streamlined workflows, and stronger outreach could improve CAB-LA delivery and help SSPs expand access to this important HIV prevention option.

Introduction

HIV disproportionately impacts PWID, with injection drug use contributing to 11% of new HIV infections worldwide.^1,2 Preexposure prophylaxis (PrEP) is a vital intervention for preventing HIV acquisition, yet uptake among PWID remains low, with structural and individual-level barriers limiting access and adherence to traditional daily oral PrEP regimens. ³ In 2018, only a quarter of PWID at risk for HIV were aware of PrEP to prevent HIV, and a mere 1% reported currently taking it. ⁴ While more recent evidence suggests PrEP awareness may be increasing, utilization among PWID remains extremely low.^5,6

Long-acting injectable cabotegravir (CAB-LA), approved by the FDA in 2021, represents a promising alternative to oral PrEP, offering sustained protection against HIV through bimonthly injections. ⁷ Clinical trials have demonstrated CAB-LA's safety, tolerability, and efficacy for sexual HIV transmission prevention, as well as higher efficacy compared to daily oral PrEP, potentially due to improved adherence to injections compared with pills.^8,9 However, CAB-LA's global roll-out has been slow due to high costs, regulatory barriers, and supply chain limitations.^10–12 In the United States, adoption has been very limited, largely due to financial and logistical hurdles; in 2023, CAB-LA accounted for only 2.7% of all PrEP prescriptions with less than 14 000 users nationwide. ¹³ This trend is particularly true among PWID, in part due to their exclusion from clinical trials and the current lack of FDA approval for parenteral HIV exposure.

Meanwhile, a growing body of evidence has demonstrated the acceptability of CAB-LA for HIV prevention among PWID.^14,15 Many PWID view long-acting PrEP as a more convenient and discreet option than oral PrEP, offering relief from barriers such as daily pill-taking and safeguarding medication while experiencing homelessness.^16–26 Additionally, some PWID find CAB-LA appealing due to its resemblance to extended-release formulations of medications for substance use disorders. ¹⁶ Nevertheless, there are likely numerous barriers to PWID's uptake of CAB-LA. At the individual-level, these include the need for frequent clinic visits and the importance of retention in care to prevent viral resistance, logistical challenges in navigating the healthcare system, financial constraints, mistrust of healthcare systems, concerns about injection site reactions and/or interactions with substance use, and the “triggering” impact of injections.^{18,19,21,23,24,27}

Research centered on CAB-LA among PWID has largely focused on individual-level perspectives, with limited evidence to date on strategies to overcome the structural and organizational factors that influence implementation, including stigma and discrimination, as well as staffing, storage, and spacing constraints. ¹¹ SSPs, as trusted and frequented venues for PWID, are well-positioned to address many of these challenges. They offer an increasingly wide range of co-located and on-demand services to PWID, including syringe exchange, overdose prevention, and linkage to care for HIV and other infectious diseases, in a low-barrier, stigma-free environment.^17,18 However, as of 2022, only 38% of SSPs in the United States provided any formulation of PrEP onsite, with competing priorities and resource constraints often shaping service delivery. ²⁸ While other researchers have hypothesized that provider knowledge and operational constraints, such as personnel shortages and financial limitations, may limit CAB-LA's roll-out in these settings, to our knowledge, there are no existing studies on SSP staff perspectives from real-world experience. ²⁵

To address this gap, research is needed to explore implementation determinants for CAB-LA in the unique operational context of SSPs and identify strategies to improve implementation. ¹⁷ This qualitative study explores the experiences of various staff implementing CAB-LA within an SSP in Philadelphia, PA. It utilizes the Consolidated Framework for Implementation Research (CFIR) to identify key implementation determinants (ie, barriers and facilitators) associated with the innovation, outer setting, inner setting, individual characteristics, and the implementation process. ²⁹

Methods

Setting

This study was conducted at Prevention Point, an SSP in the Kensington neighborhood of Philadelphia. Prevention Point is a multiservice harm reduction agency that has offered syringe services since 1991 and is now the largest SSP in the mid-Atlantic region of the United States, distributing over 7 million syringes in 2024. Over the last 30 years, its service offerings have expanded to include overdose prevention and reversal training; HIV and HCV testing, treatment, and prevention; medications for opioid use disorder (MOUD); wound care; housing services; homeless outreach; meals; mail services; police assisted diversion; case management; and navigation to other services. Prevention Point began offering CAB-LA to clients in March 2022, approximately 4 months after it received FDA approval. In 2024, the organization administered a total of 660 doses of CAB-LA to 244 unique individuals (174 women, 70 men).

Data Collection

The study was approved by the Drexel University and Philadelphia Department of Public Health Institutional Review Boards (protocol #2301009695 and #2023-26, respectively), as well as the Prevention Point Philadelphia Research Committee. It follows the Consolidated Criteria for Reporting Qualitative Research (COREQ, see Supplemental File S1). ³⁰ We conducted in-depth, semistructured interviews with a purposive sample of 12 current and former staff members at the SSP from August 2023 to July 2025, out of a total of 26 staff involved with the implementation of CAB-LA. Staff members currently or recently (within 6 months) employed by Prevention Point and involved in CAB-LA implementation were eligible for the study. Staff represented a range of roles related to CAB-LA service delivery. Clinicians included nurse practitioners, physicians, and phlebotomists who conducted clinical assessments, laboratory testing, and CAB-LA injections. Program administrators oversaw HIV prevention operations, coordinated PrEP services, managed pharmacy and insurance workflows, and supervised frontline staff. Nonclinical service providers included HIV testing counselors, medical reception staff, and PrEP navigators who were responsible for client engagement and outreach, rapid HIV testing and PrEP referrals, appointment coordination, education, and follow-up. Although not all participants directly administered injections, each held responsibilities integral to CAB-LA delivery and thus provided insight into operational, logistical, and client-facing components of implementation. We approached all eligible staff in-person or via email and informed consent was obtained prior to research activities.

Interviews took place in-person in a private location or over Zoom and were conducted by 2 female research team members (ECM, MA and AMR, PhD) with training in qualitative methods and familiarity with the SSP's staff and participants. Because the study was conducted within a single SSP with a relatively small and highly identifiable workforce, we intentionally limited the demographic variables collected to avoid compromising participant confidentiality. The interview guide was developed using the updated CFIR framework, which is widely used to assess implementation barriers and facilitators. ²⁹ For example, to explore barriers and facilitators related to the CFIR's Inner Setting domain, we asked questions regarding the service environment (including workflows, organizational culture, etc), staffing, physical infrastructure, and resource availability (see Supplemental File S2). Other domains were similarly investigated and are presented systematically in our results (see Table 2). Interviews lasted around one hour and participants received a $50 gift card as compensation for their time. The interviews were audio-recorded, transcribed verbatim in English by a professional transcription service, deidentified, and reviewed for accuracy by a member of the research team (ECM). No repeat interviews were conducted and transcripts were not returned to participants for comment/correction.

Data Analysis

We analyzed transcripts using thematic analysis, which involves systematically identifying, organizing, and interpreting key patterns and themes that emerge from the data. ³¹ Using Dedoose (version 9.0.107, Sociocultural Research Consultants, Los Angeles, CA), 2 team members (MP and EF) reviewed 2 transcripts and reached consensus on a structured codebook based on the CFIR constructs, with minor modifications subsequently added during analysis of additional transcripts. The same 2 team members then analyzed all remaining transcripts simultaneously and in duplicate. Differences in coding were discussed until consensus was reached and the team deemed the analysis to have met thematic saturation. Through examination with the broader team, the codes were then condensed and translated into themes within each of the CFIR domains (ie, Innovation, Outer Setting, Inner Setting, Individual Characteristics, and Implementation Process) and constructs (see Table 2 for definitions). The team then made an interpretive decision about whether each theme served as a barrier or facilitator for the implementation of CAB-LA in the SSP setting. Data (ie, exemplar quotes) were identified to highlight each theme.

Results

Selected sociodemographic characteristics of the participants are provided in Table 1. Participants had a median of 2.5 years of experience at the SSP and worked as clinicians (42%), program administrators (25%), and nonclinical service providers (33%).

Table 1.

Sociodemographic Characteristics of Participants.

Characteristica	Total Sample (N = 12)
Role at the SSP (n, %)
Clinician	5 (41.7)
Program administrator	3 (25.0)
Nonclinical service provider	4 (33.3)
Years of experience at the SSP (median, IQR)	2.5 (3.81)

SSP, syringe services program.

In the following sections, themes regarding the implementation of CAB-LA at the SSP are presented in their respective CFIR domains: Innovation, Outer Setting, Inner Setting, Individual Characteristics, and Implementation Process (Table 2). Each theme is related to a CFIR construct and identified as either an implementation facilitator or barrier.

Table 2.

Themes and Exemplar Quotes, by CFIR Domain and Construct.

CFIR Domain	CFIR Construct	CFIR Construct Definition	Theme	Barrier or Facilitator
Innovation	Innovation Relative Advantage	The innovation is better than other available innovations or current practice.	CAB-LA offers numerous advantages over oral PrEP for PWID.	Facilitator
	Innovation Evidence-Base	The innovation has robust evidence supporting its effectiveness.	No data are yet available on the use of CAB-LA among PWID.	Barrier
	Innovation Complexity	The innovation is complicated, which may be reflected by its scope and/or the nature and number of connections and steps.	Logistical requirements for CAB-LA (e.g., testing requirements, insurance verification, medication sourcing) are more complex than oral PrEP.	Barrier
Outer Setting	Partnerships and Connections	The Inner Setting is networked with external entities, including referral networks, academic affiliations, and professional organization networks.	Technical support from external partners is helpful for training staff, sourcing CAB-LA, and engaging clients.	Facilitator
	Financing	Funding from external entities (e.g., grants, reimbursement) is available to implement and/or deliver the innovation.	Revenue from a 340B pharmacy is critical to implement CAB-LA in a low-resource setting.	Facilitator
	External Pressure (Performance-Management)	Quality or benchmarking metrics or established service goals drive implementation and/or delivery of the innovation.	Stringent monitoring and deliverable requirements sometimes conflict with the realities of serving a highly marginalized population.	Barrier
Inner Setting	Mission Alignment and Culture (Recipient-Centeredness)	Implementing and delivering the innovation is in line with the overarching commitment, purpose, or goals in the Inner Setting. There are shared values, beliefs, and norms around caring, supporting, and addressing the needs and welfare of recipients.	CAB-LA is well-aligned to the SSP's mission and values of meeting people where they are with a one-stop shop of harm reduction services.	Facilitator
	Compatibility	The innovation fits with workflows, systems, and processes.	CAB-LA is compatible with the SSP's existing services and workflows.	Facilitator
	Physical Infrastructure	Layout and configuration of space and other tangible material features support functional performance of the Inner Setting.	Limited physical space at the SSP hinders the efficient provision of CAB-LA.	Barrier
	Relative Priority	Implementing and delivering the innovation is important compared to other initiatives.	CAB-LA struggles to compete with other SSP services for provider time and institutional priority.	Barrier
Individuals	Innovation Deliverers (Motivation)	The individuals who are directly or indirectly delivering the innovation are committed to fulfilling their role.	SSP staff play a crucial role in championing low-barrier PrEP services and ensuring the successful roll-out of CAB-LA.	Facilitator
	Innovation Deliverers (Capability)	The individuals who are directly or indirectly delivering the innovation have the interpersonal competence, knowledge, and skills to fulfill their role.	SSP staff require structured, formal training on CAB-LA implementation.	Barrier
	Innovation Deliverers (Opportunity)	The individuals who are directly or indirectly delivering the innovation have the availability, scope, and power to fulfill their role.	CAB-LA substantially increases caseloads and workload for an already overburdened staff.	Barrier
	Innovation Recipients (Opportunity)	The individuals who are directly or indirectly receiving the innovation have the availability, scope, and power to fulfill their role.	Client service engagement with SSP services and the clinic's drop-in model of care creates challenges for retention in CAB-LA care.	Barrier
Implementation Process	Engaging	Attract and encourage participation in implementation and/or the innovation.	Financial incentives are critical to increasing client engagement and retention with CAB-LA.	Facilitator
			The SSP's limited outreach with CAB-LA services limits client engagement to those who visit the fixed site.	Barrier

PWID, people who inject drugs; CAB-LA, long-acting injectable cabotegravir; CFIR, Consolidated Framework for Implementation Research; PrEP, preexposure prophylaxis; SSP, syringe services programs.

Innovation (ie, CAB-LA)

CAB-LA's relative advantage over oral PrEP (CFIR Construct: Relative Advantage) emerged as a major facilitator of implementation. SSP staff expressed strong enthusiasm for CAB-LA, calling it a “godsend” and a “game-changer” (nonclinical service providers) for their clients. They highlighted its ability to circumvent patient-level structural and social barriers to care, particularly for clients struggling with adherence to daily oral PrEP due to unstable living conditions. As one staff member explained, “there's a lot of barriers to actually taking your oral PrEP effectively” (clinician), including “remembering to take it every day” (nonclinical service provider), “the ability to hold on to your medication” (clinician), and “people's safety, like constantly getting robbed” (clinician). Another staff member added, “they don't have homes. They lose their medication. They forget to take them” (nonclinical service provider). CAB-LA's long-acting formula also reduced the frequency of clinic visits, making it a low-barrier option. As one staff member explained, “They come in. They see a provider. They get the injection. They get an incentive. They go, and we don’t see them for another two months” (nonclinical service provider). CAB-LA was described as “more reliable” (clinician), “easier” (program administrator), and “convenient” (nonclinical service provider) than oral PrEP because it “meets people where they are” (clinician). Its streamlined process enhances the client experience while also increasing the SSP's capacity: “I had to do less frequent check-ins with people, which opened up the capacity to see a larger amount of people” (nonclinical service provider). Lastly, staff commented that CAB-LA had minimal side effects (“just injection site pain” (program administrator)) compared to oral PrEP, which left some clients “throwing up their guts” or feeling “really uncomfortable” (program administrator). They noted that CAB-LA may offer a safety advantage over oral PrEP for clients with kidney disease, since oral tenofovir-based PrEP is contraindicated in this population. At the same time, they cautioned that CAB-LA does not treat hepatitis B coinfection, unlike tenofovir, though some viewed this as potentially advantageous in avoiding the risk of liver inflammation that can occur when starting and stopping antihepatitis B treatments.

Conversely, the limited evidence base for the use of CAB-LA among PWID (CFIR Construct: Evidence-Base) was described as a barrier. Staff voiced concerns about the lack of FDA approval of CAB-LA for parenteral transmission of HIV, which created clinical uncertainty for providers: “Because it's not indicated for PWID … it's off-label, so that can be just tough” (clinician). Staff also perceived clients to be wary: “A lot of patients … don't want to be experimented on” (program administrator). Staff expressed uncertainty about CAB-LA's time to effectiveness, explaining, “We don’t really know how long it takes to become effective” (clinician). Nonetheless, providers remained committed champions of CAB-LA, stating“Unless there is an act of God or Congress tomorrow that says [I] cannot deliver [CAB-LA to PWID] … I'm going to continue doing it” (clinician).

Finally, the complexity of getting patients started on CAB-LA (CFIR Construct: Complexity) emerged as another major barrier. Staff described multiple logistical hurdles involved in prescribing CAB-LA—including testing and phlebotomy requirements, insurance verification, and medication ordering protocols—which created delays in treatment initiation. “Same-day starts are somewhat impossible” (clinician), as confirmatory HIV results are required before initiation. Even under the current streamlined process, the timeline from expressing interest to first injection typically takes “anywhere from 48 hours to a week” (clinician). Staff noted that while this reflects a meaningful improvement from earlier workflows that required multiple provider appointments before CAB-LA initiation, these delays still pose significant barriers to patient uptake, engagement, and retention. Insurance further complicated access, as staff “often can't get information [from clients] in a timely manner” (program administrator). Recounted one staff, “I [tried to] call and be like, ‘Hey, so-and-so insurance is cut off. Turn it back on.’ [The insurance representatives] were like, ‘Well, we need to speak to so-and-so.’ And [I’m] like, ‘So-and-so disappeared'” (program administrator). Supply issues added further delays: “There were a lot of times where the injections weren’t there at our physical location” (clinician). Staff described how these logistical hurdles impeded client engagement: “By the time [the medication arrives], we lose somebody … they stop engaging because things are taking too long” (nonclinical service provider). Considering that most clients rely on incentives, these delays had an even greater impact: “They’re also not getting paid now. It's like a double smack to the face” (nonclinical service provider). Staff proposed solutions to reduce delays in initiating PrEP, such as oral lead-ins, ordering medications at the same time as labs, and maintaining a reserve supply.

Outer Setting (ie, the Broader Context Within Which the SSP Operates)

Partnerships and connections with external organizations (CFIR Construct: Partnerships and Connections) facilitated CAB-LA implementation, especially given its novelty and logistical complexity. “They had someone from the manufacturer come out and give a really good training” (clinician), one staff member recalled. Another added, “They did an in-service with us, taught us how to prepare and administer the injections” (nonclinical service provider). Likewise, the clinician PrEP hotline offered by CAB-LA's manufacturer was valued: “I would use [it] to have another backup person, and that gave me a lot more confidence” (clinician). Staff who were initially skeptical about CAB-LA's feasibility found that ongoing support from these external partners helped shift their perspective: “I [thought] this isn’t going to work … getting people injected would be such a hassle … But the more training that we got … changed my mind” (program administrator). External research partners who were recruiting for an ongoing PrEP-related study for women who inject drugs also played a crucial role by conducting outreach and client retention activities that the SSP “didn’t have the capacity to do” (nonclinical service provider). ³² While this was related to a research study, SSP staff expressed that this support was particularly important for engaging with specific client populations, “especially for our female clients … they know that there are a group of people that are very supportive of them and just trying to help” (program administrator). Finally, staff emphasized the importance of their strong, collaborative relationship with the local pharmacy, which helped them navigate prescribing and supply chain challenges. The pharmacy also facilitated medication delivery: “They ship, and they deliver our [CAB-LA] to us as needed” (program administrator).

The availability of financing through the 340B pharmacy partnership (CFIR Construct: Financing) also served as a crucial facilitator. Staff described this partnership as essential for stretching resources and expanding access to CAB-LA for uninsured clients, because “it's really, at the end of the day, about resources” (program administrator). Said one staff, “There were a lot of pros to using the 340B Program because we're working with such an underserved population” (clinician). Despite this, staff noted that existing funding levels limited “how much time [the SSP] could buy from a provider” (program administrator) for onsite service delivery, as well as which clients were eligible for CAB-LA, since clients were not “able to get on [CAB-LA] unless they had insurance” (program administrator). (The 340B Drug Pricine Program is a national program that allows eligible healthcare organizations to purchase outpatient drugs at significantly reduced prices to expand services for low-income and underserved populations.)

Meanwhile, external performance-management pressures (CFIR Construct: External Pressure—Performance-Management) were identified as a barrier. Staff explained that the stringent monitoring and deliverable requirements associated with public funding conflicted with the realities of serving the SSP's clients. They emphasized, “In this [kind of work], sometimes outcomes are slow” (program administrator). Explained another, “You have to manage expectations around what the outcomes are going to look like” (program administrator). The emphasis on adherence metrics, in particular, posed difficulties with CAB-LA: “So, we have to link a certain number of folks to PrEP … but if only 20 of them are adhering, then we’re not meeting our deliverables” (program administrator). These tensions were compounded by the SSP's drop-in clinic model, which is intentionally structured to accommodate the acute needs and unpredictable schedules of its clients, including periods of hospitalization, incarceration, and competing survival priorities. While this flexibility is essential for client-centered care, it means that rigid adherence metrics and service targets set by funders often clash with the realities of delivering low-barrier services.

Inner Setting (ie, the SSP)

Strong mission alignment and shared values (CFIR Construct: Mission Alignment and Culture—Recipient-Centeredness) between the aims of CAB-LA and the SSP facilitated its implementation. Staff described the SSP as “the perfect place” (clinician) to offer CAB-LA, due to its “110% alignment” (clinician) with their harm reduction mission and its goal of serving as a “one-stop-shop” (clinician). As one staff member explained, “it's so hard for [PWID] to engage in care” (clinician) when they’re treated as “just another number, another chart” (program administrator), and many providers “don’t see anything other than [their] substance use” (clinician). They observed that the system “places blame on the patient” (program administrator) rather than addressing the structural and socioeconomic barriers that hinder engagement and retention in care. In contrast, SSP staff “understand what people's lives are like” (clinician) and “create relationships with them” (program administrator) which builds trust. CAB-LA, likewise, “takes the burden off the patient” and “sets people up for success in a way that we couldn't before” (clinician). Alongside this, the addition of CAB-LA to the SSP's PrEP offerings also aligned with the organization's culture of client-centeredness: “It really just depends on the person's preference” (program administrator). Staff emphasized the importance of promoting autonomy for a population that often lacks agency: “Our [clients] don't have a lot of choices … and so, giving them a choice like that is important” (clinician).

Compatibility with existing workflows and the SSP's previous experience delivering long-acting medications (CFIR Construct: Compatibility) also emerged as a facilitator. CAB-LA was described as a natural “addition to the menu” (program administrator) of the SSP's existing “status-neutral approach to HIV” (clinician) services. ³³ (A status-neutral approach to HIV service delivery uses the same approach for client engagement and retention, regardless of one's HIV status. It functions as a continuous, high-quality care loop that provides people with the tools they need to stay healthy and help prevent HIV transmission.) Staff emphasized that the SSP's services and personnel already “work hand in hand” (nonclinical service provider), making the organization “really well-positioned to increase the amount of people that [use CAB-LA] without a lot of changes” (clinician). Additionally, the SSP's “success with other long-acting injectables” (clinician), such as long-acting medications for opioid use disorder (MOUD), gave them confidence that they could find a way to integrate CAB-LA into existing workflows.

In contrast, limited physical infrastructure at the SSP (CFIR Construct: Physical Infrastructure) was a significant implementation barrier. Explained one staff, “As far as space, there is none” (program administrator). Even when space was available, inefficient layout and workflow disrupted operations, leading to client frustration: clients are “left in the hallways, and it's never really clear where they're at in the process” (clinician). As a result, “patients are asked over and over again, ‘Where are you at? Are you waiting on me?'” (clinician).

Additionally, the relative priority of CAB-LA compared to other services (CFIR Construct: Relative Priority) also constrained implementation. Some staff felt that CAB-LA struggled to compete with other SSP services for provider time and institutional priority: “PrEP is not a life-saving drug, right? It's preventative … so, at the moment, it feels like the PrEP program is fighting for provider time” (program administrator).

Individual Characteristics (ie, the Characteristics of the SSP's Staff and Clients)

Staff motivation and commitment to delivering CAB-LA (CFIR Construct: Innovation Deliverers—Motivation) were strong facilitators. Staff described how they championed CAB-LA implementation and felt that they played a crucial role in ensuring its successful roll-out. Their perseverance and patience were essential to overcoming initial challenges. One staff reflected, “It all comes down to time and patience” (clinician).

However, limited training and preparation (CFIR Construct: Innovation Deliverers—Capability) were barriers to implementation. Although staff were highly skilled in harm reduction and clinical care, many lacked formal training on CAB-LA implementation: “There was honestly minimal PrEP training … it was mostly just hands-on as people came in, figuring it out as I go” (nonclinical service provider). One staff recalled that “people had questions that we didn't know the answer to” (program administrator). Another described how their supervisor “got us as many trainings as he could,” but added, “the standard, yearly PrEP trainings haven’t really been updated in a while” (nonclinical service provider). They felt that “if there was more of a set training schedule … it would have been a more cohesive transition” (nonclinical service provider).

Heavy workloads and role strain (CFIR Construct: Innovation Deliverers—Opportunity) were also important barriers. CAB-LA significantly increased the caseload for an already strained staff. They explained that, within the SSP, they were already responsible for “at least six or seven different roles” (nonclinical service provider). With the addition of CAB-LA, workloads were described as overwhelming, with one staff member stating, “We were running around like chickens with our heads cut off” (nonclinical service provider). This impacted patient care: “If you’re at max capacity and you don’t have the people to staff it or the resources for your staff, then you’re going to be sacrificing quality of care” (nonclinical service provider). As a result, there was “burnout every single day” (program administrator), especially because of the emotional toll of working with the SSP's clients: “when a client comes in and just dumps a bunch of trauma at 9:00 AM, and I have a whole day to complete, I have to harbor what [they] just [said]” (nonclinical service provider). High staff turnover further complicated implementation, as it disrupted relationships with clients who relied on consistency in care: “[Clients] get so upset when somebody leaves … and sometimes they fall out of care because of that. It's a lot of work to really gain people's trust” (clinician).

Finally, client service engagement (CFIR Construct: Innovation Recipients—Opportunity) created challenges for retention in CAB-LA care. Staff described how competing survival needs, health crises, hospitalizations, and periods of incarceration often affect whether and when clients can access services. As one staff member explained, “Our patients sort of just stroll in when they remember or when they’re in the area” (program administrator). To accommodate these barriers to service engagement, the SSP's clinic is intentionally structured as a drop-in model. While essential for client-centered care, this service delivery model can make clinic flow unpredictable: “One minute it could be cool, calm, collected, next minute it could be chaotic” (nonclinical service provider). The flexibility of this model is not typically problematic for services like syringe exchange or wound care; however, staff said that it created challenges for maintaining CAB-LA continuity and avoiding viral resistance, given the innovation's specific dosing and labwork schedule: “Some are really, really good at keeping up with their care,” one staff member explained, “and then we’ll see [others] probably like once every three to six months” (clinician). Notably, there were mixed opinions on whether a longer-acting CAB-LA formulation would improve adherence. Some staff believed that “to just have to do that once every six months would probably be really good” (nonclinical service provider), citing reduced burden on clients and staff alike. Others, however, worried that six months would be “entirely too long” (clinician) given the challenges of follow-up and maintaining service engagement with this population. Staff proposed appointment cards and frequent reminders to improve follow-up.

Implementation Process (ie, the Process of Implementing CAB-LA at the SSP)

The use of financial incentives ($50 gift cards provided for each CAB-LA injection received; CFIR Construct: Engaging) was identified as a crucial facilitator for engaging clients and ensuring retention, as they addressed clients’ immediate needs. Staff emphasized, “We’re not [coercing them]. We’re just allowing them to live by providing their next meal, and also preventing them from getting a communicable disease” (clinician). Said another, “I think from a public health standpoint, it's the best thing we can do. We get people in the door” (clinician).

Conversely, the limited outreach of CAB-LA services (CFIR Construct: Engaging) was described as a barrier to client engagement. Staff saw mobile outreach—bringing services directly to clients in the community, such as through vans or street-based engagement—as “the next piece of where PrEP needs to go within the programs,” especially given that “there are people who have been using our services for years that never walked into our building” (program administrator). However, they cautioned that successfully expanding PrEP services through outreach would require additional staffing and intensified follow-up efforts.

Discussion

This study provides real-world insights into the delivery of CAB-LA for PWID at a low-barrier SSP, highlighting key facilitators and barriers within each CFIR domain. Staff described the innovation's relative advantage, emphasizing how CAB-LA reduced the daily burden on clients and offered a more feasible PrEP option for individuals who face challenges with oral PrEP adherence. The recipient-centeredness of the SSP's model and the mission alignment between CAB-LA and harm reduction principles enabled strong buy-in from staff. An overarching challenge for CAB-LA implementation was the low-barrier clinic model that allowed clients to present for services without an appointment. In the context of a population with complex health needs, having time to address PrEP, and CAB-LA specifically, posed challenges; staff described clients sometimes leaving before receiving services, presenting late, or entirely missing prescheduled appointments. All of these challenges caused delays and increased staff burden. Compatibility with existing workflows, experience with other long-acting injectable medications, technical support from external partners, and revenue from a 340B pharmacy partnership provided logistical and financial support that further facilitated implementation, and financial incentives enhanced client engagement. However, in the context of a low-barrier clinic, CAB-LA's complexity, including testing protocols, insurance requirements, and medication procurement, caused delays and additional strain on staff who already held multiple roles and faced heavy workloads. Challenges with physical infrastructure and relative priority within the SSP also constrained smooth delivery. Additionally, limited staff capacity made outreach and retention difficult, while performance-management pressures and lack of formal training contributed to burnout and uncertainty. Staff also noted that the absence of FDA approval for use among PWID—reflecting a limited evidence base for the innovation with this population—posed clinical dilemmas for providers. Still, this study demonstrates that even in the face of significant organizational and systems-level barriers, CAB-LA can be integrated into SSP settings through strong mission alignment, provider commitment, and targeted adaptations that continue to evolve with experience.

Interestingly, these findings suggest that CAB-LA's perceived value among SSP staff stemmed less from its superior efficacy compared to oral PrEP and more from how it shifted the burden of adherence away from clients. CAB-LA's relative advantage was thus framed in terms of feasibility and fit within clients’ lives, rather than pharmacologic outcomes alone. Staff overwhelmingly expressed willingness to take on additional work as a tradeoff to ease care experiences for their clients. At the same time, the findings highlight that high acceptability—even among motivated staff—is not enough to ensure smooth implementation. Compounding effects of organizational and structural barriers limited what was feasible in practice, emphasizing the need to address system-level constraints alongside individual-level enthusiasm.

These findings are consistent with and build upon existing literature. Previous studies have described the hypothetical or anticipated acceptability of CAB-LA among PWID, often citing preferences for long-acting formulations due to their alignment with client needs and experiences.^{14,16–22,24,25} This study moves beyond perceived acceptability to document real-world implementation determinants in the SSP setting, providing post-implementation evidence of staff perspectives on successes and operational challenges. The interaction between multiple barriers echoes prior research on PrEP implementation for marginalized populations, where individual, interpersonal, organizational, and systems-level barriers often overlap and compound,^{18,19,21,23,24,27} suggesting that implementation strategies must be developed and tested that are multilevel and multicomponent.

Our findings have important implications for both programs and policy. SSPs considering CAB-LA implementation should anticipate the need for expanded staff capacity, targeted, context-specific training, and systems to support medication procurement and sustained client engagement for care follow-up. Because staff uncertainty often reflected unclear or evolving workflows rather than gaps in clinical knowledge, training may be most effective when paired with implementation strategies that make workflows visible, such as group-based process mapping, clarifying handoffs between roles, and identifying bottlenecks, to support redesign of procedures within each unique setting. Such approaches can help ensure that each staff member understands where CAB-LA fits within their existing responsibilities, which tasks require coordination across teams, and how to adapt when client engagement is unpredictable. Programs may also benefit from integrating CAB-LA into existing workflows for long-acting MOUD, and leveraging 340B partnerships to support access for uninsured clients. Funders of SSPs should modify performance metrics to account for the realities of serving PWID, avoiding overly rigid adherence targets that don’t adequately account for the challenging work of reaching individuals who would otherwise be unengaged. Several adaptations identified in this study, such as concurrent ordering of labs and CAB-LA, and improved supply management, have already been implemented and are beginning to reduce delays in initiation, illustrating the importance of continuous learning and iteration in early-phase roll-out.

This study has several strengths. It is the first study, to our knowledge, to explore real-world CAB-LA implementation in a harm reduction setting. The inclusion of both clinical and nonclinical staff perspectives enriched the analysis and reflects the reality of service delivery in low-resource programs, such as SSPs. Use of the CFIR allowed us to systematically identify multilevel implementation determinants, grounded in a robust and respected theoretical framework. Finally, the study team was composed of individuals with personal experience working at SSPs, allowing for context-sensitive insights; likewise, our close engagement with the SSP enabled the findings to be used to support additional programmatic adaptations.

With regard to limitations, first, this study reflects the experiences of a single, comparatively well-resourced SSP with access to external support from academic and pharmaceutical partners. These characteristics may limit the transferability of findings to SSPs operating with fewer resources and/or in less supportive environments. In particular, SSPs in nonurban or less resourced settings—where staffing structures, access to colocated clinical services, and pharmacy or technical partnerships may differ—may encounter distinct operational challenges and require different adaptations for CAB-LA delivery. However, because this was a qualitative, single-site study, the findings are not intended to be generalizable but rather to provide in-depth insights into early-phase implementation. Additionally, several cross-cutting determinants identified here, such as the need for workflow clarity, tailored training, and strategies to support client engagement, are likely relevant across diverse SSP models. Second, only 12 of the 26 staff directly involved in CAB-LA implementation participated in the study, which may have excluded perspectives from certain roles; this partial sample should be considered when interpreting the findings. Additionally, participant checking of the analysis was not conducted. Third, interviews were conducted at a single point in time and therefore may not capture the ongoing adaptations the SSP continued to make in response to its shifting context. Finally, while this analysis focused on staff perspectives, it did not include those of PWID; this is an important gap given that client engagement and retention are critical. However, complementary client-focused research is underway; for example, a recently published qualitative study from the same SSP examined why women who inject drugs chose CAB-LA over daily oral PrEP, offering critical insights from the client perspective. ¹⁵

Conclusion

This study reiterates the potential of CAB-LA as a highly promising HIV prevention tool for PWID, and demonstrates that SSPs are uniquely positioned to deliver it when supported by mission alignment, committed staff, and adaptable workflows. Yet successful implementation requires more than enthusiasm; the complexity of CAB-LA delivery, combined with structural constraints, resource limitations, and the realities of serving a marginalized population, underscores the need for sustained investment and systems-level support. By addressing these multilevel barriers and leveraging existing strengths within SSPs, programs can enhance equitable access to long-acting PrEP and move closer to reducing HIV transmission among PWID.